Formally present active infinitive corresponding to fui(“I have been”), irregular perfect indicative of sum(“I am”). From Proto-Indo-European*bʰuH-(“to become, be”), cognate with Old Englishbēo(“I become, I will be, I am”). In classical Latin, the fu- forms of sum are mostly limited to the perfect tenses, but old Latin has alternate present and imperfect subjunctive forms fuam and forem (for classical sim and essem) suggesting the root could once be fully conjugated. After being incorporated in the conjugation of sum, the meaning of fore shifted from the original "to become" to the classical "to be going to be".